You're gonna' be surprised just how easy it is to accurately test the mass air flow (MAF) sensor on your 2.0L Mazda 626 (2.0L Mazda MX6) with a multimeter. That's right, you don't need a scan tool for the MAF sensor test described in this tutorial.

Symptoms Of A BAD MAF Sensor

The MAF sensor's role is to help your Mazda's fuel injection computer know how much air is entering the engine. With this info, the computer can now calculate the correct amount of fuel to inject into the 4 cylinders.

One of the following diagnostic trouble codes (DTCs) is lighting up the check engine light:

P0101: MAF Sensor Performance.

P0102: MAF Sensor (MAF) Low Input.

P0103: MAF Sensor (MAF) High Input.

Doesn't pass the smog check.

Engine idles rough.

Engine takes forever to start (extended cranking time).

Engine doesn't start.

Black smoke coming out of the tail-pipe as engine runs.

MAF Sensor Circuit Descriptions

The MAF Sensor, on your 2.0L Mazda 626, has 4 wires coming out of its connector. Each wire has a specific job to and thus carries a specific signal.

If you take a close look at your MAF sensor (and if it still has an original MAF sensor), you'll notice that that are 4 letters embossed on it, near its connector. These letters are A, B, C, and D. These letters identify specific circuits:

To test these circuits, we'll have to use a back-probe or a wire piercing probe the wire of the connector. Probing the front of the connector's female terminal with a multimeter's test lead can damage it. You can take a look at what a wire piercing probe looks like here: Wire Piercing Probe Tool Review (Power Probe PWPPPPP01)

TEST 1: Checking The MAF Sensor Signal

The key to diagnosing a bad MAF sensor is to know that its voltage signal increases with increased air flow (like when you step on the accelerator pedal) and decreases as that air flow slows down (like when you step off of the accelerator pedal).

With a multimeter, we can tap into the MAF signal wire and observe theses voltage changes as we rev the engine up and down.

If the MAF sensor has failed on your 2.0 Mazda 626, it will not produce a voltage signal that increases or decreases when you rev up the engine. In other words, the bad MAF sensor will show a voltage that will stay stuck in one value (on your multimeter) no matter the amount of air the engine is breathing.

NOTE: Be careful and take all necessary safety precautions! The MAF test in this section is done with the engine running in your 2.0L Mazda 626 (2.0L Mazda MX6).

NOTE: The MAF sensor is tested with it connected to its electrical connector, so don't remove it or unplug it (from its electrical connector). The illustration above shows the MAF sensor unplugged and removed just to make it easier to explain the test.

Alright, these are the test steps:

1

Set the multimeter to Volts DC mode and probe the PNK/BLK wire of the MAF sensor connector with the red multimeter lead.

The pink with black stripe (BLK/PNK) wire is the one that connects to MAF sensor pin D in the illustration above.

NOTE: Since the MAF sensor has to remain connected to its electrical connector, you'll need to use a tool like a wire piercing probe to access the signal inside the wire. To see what a wire piercing probe looks like, go here: Wire Piercing Probe.

2

Ground the BLACK multimeter test lead directly on the battery negative terminal.

3

Have a helper start the engine. Wait for the engine's idle to stabilize and observe your multimeter's voltage reading.

With the engine idling, the voltage reading should be about 1.5 to 1.8 Volts DC.

Now, have your helper accelerate the engine. The voltage should increase.

At around 4,000 RPMs, the multimeter should register to about 3 Volts DC.

4

Decelerate and accelerate the engine several times as you observe the multimeter

Your multimeter should register a decrease/increase in voltage as you decelerate/accelerate the engine if the MAF sensor is good.

If the MAF sensor is bad, the voltage will be stuck at a certain number no matter how much you accelerate/decelerate the engine.

OK, let's take a look at what your MAF sensor test results mean:

CASE 1: The MAF sensor produced and increasing/decreasing voltage signal as you accelerated/decelerated the engine: This tells you that the mass air flow sensor is OK (not defective).

CASE 2: Your multimeter registered voltage, but it did not increase or decrease as you accelerated/decelerated the engine: This usually confirms that the mass air flow (MAF) sensor on your 2.0L Mazda 626 (2.0L Mazda MX6) is BAD. Replacing the MAF sensor will solve the MAF sensor trouble code lighting up the check engine light.

CASE 3: Your multimeter registered 0 Volts: This usually means that the MAF sensor is fried. To be absolutely sure, I suggest confirming that the MAF sensor has power and its two grounds. If both (power and its two grounds) are present, the MAF sensor is BAD.